Hi Larry,
First off, I am to understand that you've already upgraded to 8GB of RAM. Secondly, I'm also going to assume that you're asking about SSD (Solid-State Drive) and have accidentally typed SSID (Service Set Identifier). Let's see if I can address your concerns:
- Upgrading to an SSD is definitely going to give you a performance boost. Based on how you use your machine the boost will more noticeable. But pretty much anyway you cut it things will be faster, more responsive and take less time to load/process. Will be considerable? That's for you to determine, a couple seconds here and a couple seconds there may or may not be enough to justify the investment that is an SSD.
- Weight-wise, replacing the conventional HD with an SSD isn't going to suddenly turn the machine into a featherweight. Obviously, as I'm sure you know, switching form factor completely from 13" MBP to 13" MBA or event 11" MBA would significantly lower the overall weight in your bag/brief case/backpack. However there's going to be a compromise.
- Speculation/rumor mills seem to be hot on the case of a MBA refresh being all but here. The initial rumors pegged a late June to early July window (Sandy Bridge, Thunderbolt, Intel GPU). More recent rumors have stated that Apple is "holding" any new hardware refreshes for Lion, which does not have a release date but a release window (July '11). Regrettably, additional speculation and "what we'd like to see speculation" is frowned upon here (and discussed in the Terms of Use). But there are numerous other websites that exist solely for that purpose. MacRumors, TUAW, etc.
- Comparing a 13" MBP at 2.66GHz with 8GB of RAM and a 3rd party SSD to any MacBook Air isn't really a fair fight on a "benchmark" level. But the 2.13GHz MBA with 4GB of RAM is very impressive for day-to-day "typical" user tasks.
Considering the cost of SSD solutions in the 256GB+ range even Apple opted to put a larger SSD solution into the Air it would carry a very significant premium and one that I suspect would put the machine out of the price point of many potential buyers. Heck it's $1200 to go a 512GB SSD in the 15" MBP.
Another option you might want to consider, it's one I've done on my 13" MBP and I know of few other posters who have done the same is a double HDD configuration.
http://eshop.macsales.com/shop/internal_storage/Data_Doubler
OWC offers it, and I've been extremely pleased with it (I have the 60GB version). But if you've got $1,000 burning a hole in your pocket they have a 480GB SSD version. 🙂
